Update'Limit your 406 MHz Testing Time
Story and Photo by H. Dean Chamberlain
permission from FAA Aviation News
FAA regulations, Title 14 Code of
Federal Regulations section 91.207(d)(4), requires that an aircraft emergency
locator transmitter (ELT) be tested annually for 'the presence of a sufficient
signal radiated from its antenna.' The Aeronautical Information Manual (AIM) in
Chapter 6, Section 6-2-5, discusses ELTs, their use, and how to test them. To
paraphrase a statement from a movie about a failed trip to the Moon, 'Folks, we
have a problem.' The FAA requires an ELT radiated test, but if the test is not
done properly, the Federal Communications Commission (FCC) might take
enforcement action against the person doing a 406 MHz ELT test.
Here is the
problem. When the FAA test requirements were written, the basic ELT was an
analog 121.5MHz unit transmitting in the aeronautical frequency band. If the ELT
being tested could not be isolated within an approved radio frequency shielded
room or container, which keeps the signal from going beyond the room or
container, a radiated test could be done within the first five minutes after the
hour. The test requirements listed the number of recommended sweeps of the
signal to minimize the risk of anyone thinking the test signal was an actual
distress alert. The person doing the test would quickly activate the ELT, listen
for its distinctive sound on a nearby aeronautical band aircraft radio or hand
held transceiver and then turn off the ELT.
method met the FAA requirement and most organizations were okay with the idea.
That was until the newer 406 MHz ELT distress beacon was developed. Part of the
problem is that instead of being in the aeronautical band, 406 MHz is a
protected international distress frequency. Plus, with a properly registered
406MHz ELT, the transmitted signal includes a digital code that can be used to
identify the owner. As a result, the FCC can track down anyone who, in its
opinion, transmits a fraudulent or non-emergency distress signal, e.g. an FAA
Since most 406
MHz ELTs include a low-powered 121.5 MHz homing transmitter, the challenge for
the person doing the annual ELT check is how to satisfy the FAA requirement
without violating the FCC regulations. Since in most cases the person doing the
testing has no way to monitor the406 MHz emitted coded signal with-out special
equipment and can there-fore only listen for the activation of the121.5 MHz
homing signal of the combined 406/121.5 MHz ELT.
Short of a
change in the regulation, the following is one means of conducting the test.
Remember, the purpose of test is to check the aircraft's installed system from
ELT transmitter to its antenna.
any ELT should follow the manufacturer's recommended procedures. If those
procedures are not available and cannot be found, the following is one procedure
that has been coordinated with the National Oceanic and Atmospheric
Administration (NOAA) which operates the United States portion of the
inter-national satellite-based search and rescue system that monitors and
processes distress beacon alerts.
Owners of 406
MHz ELTs should limit any test to less than 30 seconds. This will preclude the
satellites from receiving a signal from the 406 MHz beacon when activated to the
'ON' condition or switch position while testing the 121.5 MHz ELT portion of a
combined ELT. This will prevent the government from initiating a search and
rescue action. There have been numerous reports of unintentional activation of
the combined ELTs when periodic maintenance testing of the 121.5MHz signal is
tested to assure proper performance. Activating the 'ON' function, which is part
of the remote control panel rather than gaining access to the combined ELT and
activating the 'TEST' function, has led to violations administered from the FCC
and causes emergency responders to react in an attempt to locate a downed air
craft. If the selection to the 'ON' position is minimized to 30seconds or less,
there is sufficient time protection to prevent crossing the 50-second time
threshold for activating the 406MHz locator signal. Operators should advise
their maintenance personnel of this limitation and possible vulnerability to
violations or sanctions.
are excerpts from AIM section 6-2-5, Emergency Locator Transmitter (ELT),
dealing with testing, false alarms, and reporting.
1. ELTs should
be tested in accordance with the manufacturer's instructions. This should be
done, preferably, in a shielded or screened room or specially designed test
container to prevent the broadcast of signals, which could trigger a false
2. When this
cannot be done, aircraft operational testing is authorized as follows:
Analog 121.5/243 MHz
ELTs should only be tested during the first five minutes after any hour. If
operational tests must be made outside of this period, they should be
coordinated with the nearest FAA Control Tower or Flight Ser-vice Station. Tests
should be no longer than three audible weeps. If the antenna is removable, a
dummy load should be substituted during test procedures.
Digital 406 MHz
ELTs should only be tested in accordance with the unit's manufacturer's
are not authorized.
should be exercised to prevent the inadvertent activation of ELTs in the air or
while they are being handled on the ground. Accidental or unauthorized
activation will generate an emergency signal that cannot be distinguished from
the real thing, leading to expensive and frustrating searches. A false ELT
signal could also interfere with genuine emergency transmissions and hinder or
prevent the timely location of crash sites. Frequent false alarms could also
result in complacency and de-crease the vigorous reaction that must be attached
to all ELT signals.
cases of inadvertent activation have occurred as a result of aerobatics, hard
landings, and movement by ground crews, and aircraft maintenance. These false
alarms can be minimized by monitoring121.5 MHz and/or 243.0 MHz as follows:
(a) In flight when a
receiver is available.
(b) Before engine shut down at the end of each flight.
(c) When the ELT is handled during installation or maintenance.
(d) When maintenance is being per-formed near the ELT.
(e) When a ground crew moves the aircraft.
(f) If an ELT signal is heard, turn off the aircraft's ELT to determine if it is
transmitting. If it has been activated, maintenance might be required before the
unit is returned to the 'ARMED' position. You should contact the nearest Air
Traffic facility and notify it of the inadvertent activation.
Monitoring and Reporting
1. Pilots are encouraged to monitor121.5 MHz and/or
243.0 MHz while in flight to assist in identifying possible emergency ELT
transmissions. On receiving a signal, report the following information to the
near-est air traffic facility:
(a) Your position at the time the signal was first
(b) Your position at the time the signal was last
(c) Your position at maximum signal strength.
(d) Your flight altitudes and frequency on which
the emergency signal was heard: 121.5 MHz or 243.0 MHz. If possible, positions
should be given relative to a navigation aid. If the aircraft has homing
equipment, provide the bearing to the emergency signal with each re-ported